With continuous shortage of the earth resources and deterioration of the environment, energy saving becomes a constant pursuit for an air conditioner, a refrigerator and etc., and especially for the air conditioner of large power consumption, the energy saving goal is more urgent, so a requirement for energy efficiency standard of the air conditioner is continuously improved. In the related art, although a system energy efficiency of the air conditioner is improved and energy consumption of a compressor is reduced, it will bring another adverse effect for the air conditioner using a conventional fixed-speed compressor, that is, in winter, especially at a low ambient temperature, a system heating capacity of the air conditioner is significantly reduced.